1. Technical Field
The present invention relates to a method of measuring a gadolinia (gadolinium(III) oxide, Gd2O3) content in sintered a UO2—Gd2O3 pellet (Gd pellet) using inductively coupled plasma-atomic emission spectrometry (ICP-AES).
2. Description of the Related Art
Nuclear fuel used in nuclear power plants varies depending on the kind of atomic reactor. Currently, the nuclear fuel, which is widely useful all over the world in a light water reactor, is uranium (U)-235 concentrated to about 2˜5%. Also, natural U is used in a heavy water reactor, and U concentrated to about 26% is used as nuclear fuel in a fast breeder reactor.
In the use of nuclear fuel, a powder material of nuclear fuel is compacted in the form of a small cylinder, sintered and formed into pellets, after which the plurality of pellets thus formed is placed in fuel rods to manufacture nuclear fuel rods.
The manufactured nuclear fuel rods are collected and bundled thereafter. Then, the nuclear fuel bundles are mounted in an atomic reactor to induce fission. In the course of fission, a mass defect of atoms is converted into a large amount of thermal energy, which is then used to produce electrical energy.
In a fission chain reaction of U, neutrons cause U-235 atoms to fission. As such, two or three neutrons are emitted again. Then, the emitted neutrons cause other U-235 atoms to fission. The fission chain reaction takes place in this way. When the neutrons are generated by fission, fast neutrons having very high energy are also produced. The fast neutrons are converted into thermal neutrons having middle energy and then into thermal neutrons having low energy. The thermal neutrons having low energy then undergo once more an absorption procedure for inducing fission.
Because neutrons have no charges, they do not lose energy due to an electromagnetic action such as electrolytic dissociation when passing through a material, resulting in a high transmission capability. For this reason, neutrons are essentially used in inducing fission without being disturbed by repulsive force with atomic nuclei.
The neutrons having middle energy are highly apt to be absorbed by resonance absorption without fission. The neutrons slowly lose their energy by collision with atomic nuclei. As such, energy which is lost per collision increases in inverse proportion and the mass of atomic nucleus which is a target decreases.
This process of energy loss is called moderation, and a material which effectively causes moderation is referred to as a moderator. Specifically, in order to appropriately convert neutrons having high energy into neutrons having low energy, the moderator is used to make the neutrons collide with atomic nuclei.
Such a moderator is mainly exemplified by sintered Gd pellet (for flammable absorption rods). Whereas sintered UO2 pellet functions to generate neutrons in an atomic reactor, the sintered Gd pellet is fuel for absorbing neutrons so as to effectively control the output distribution of an atomic reactor. While the development of techniques for long-term operation of atomic power plants and highly combustible nuclear fuel continue to grow, the use of the sintered Gd pellet has recently been increasing. Such sintered Gd has been mostly dependent on importation to date, but is gaining success in localization. As such, localization requires the development of novel detection techniques and the establishment of test procedures.
Accordingly, methods of the measuring Gd2O3 content using X-ray fluorescence (XRF) have been conventionally used. Specifically, a UO2—Gd2O3 sample is dissolved in a nitric acid and then added with samarium (Sm). The prepared UO2—Gd2O3 sample is placed in a cell, and is then irradiated with X-rays as a radioactive light source and thus excited, so that elements of the sample absorb primary light rays and are thus excited, thereby emitting their characteristic type and X-rays. From Gd and Sm elements among the emitted elements, specific X-rays are counted, and spectral intensity is measured using a detector. The Gd2O3 content may be determined by a ratio of the Gd elements relative to Sm elements.
However, the above method is difficult to precisely detect the Gd2O3 content attributable to interference between U and Gd.